My husband had an affair with someone he went to highschool with

My husband struck up a conversation with someone he went to high school with hoping to fix her up with his recently divorced friend. Long story short, she wanted my husband, not the friend. They saw each other about 20 times over the course of a year. She lives about 3 hours from us. I grew suspicous over the year as he took out extra money from our account for hotel rooms, etc. He also had been more secretive and locking his phone claiming that he was keeping the kids out (they were changing his settings). One morning, I got on his phone and read his email. He didn't know enough to empty the trash and there was 2 weeks worth of email from her. That is how I found out. I confronted him and he ended the affair (in email). Her birthday was about a month later and she tried contacting him (hurt that he had not acknowledged her birthday). She then contacted me by sending me notes. My husband and I are working things out. He has blocked her from all his accounts. He was relieved that I found out. He said he regretted it from the beginning. He gave me what I consider full disclosure. She had an ugly childhood which included a drunk mother, a stint in foster care, and marriage at 16 ... baby at 17. She is divorced twice. He second husband cheated on her. He said seeing her was like seeing a prostitute but cheaper (just the cost of a hotel room and a cheap gift). He said it was a trap. She offered no-strings fun and games, then pushed for more. She drove long distances on her days off so he could get it done over his lunch hour at little or no inconvenience to him. He said she was volatile and jealous of me. Their primary source of communcation was email (mostly from her with little response from him, which frustrated her). We did have occasion to go to her home town a few times. He did treat her like a prostitute, only giving her 30-45 minutes of his "time". He did give her a weapon, but he said it was a pos he found in someone's garage. After he dumped her, she said she would "wait" for him. He laughed about that and the tattoo she got just before he dumped her of his name on her hip. She also changed her appearence and lost a bunch of weight for him. I have forgiven her. My question is, should I let her know? She sounds like she has a low self-esteem. Hopefully she won't gain all the weight she lost back. Hopefully next time, she will demand better treatment than being treated like a "prostitute".